Dynamoelectric machine commutation



Sept. 5, 1950 c.- A. THoMAs 2,521,551

DYNAIIOELECTRIC MACHINE CGMMUTATION Filed uarch 19. 1948 w 1:52.21 I3 ""4 3 la i 6W 5 ll- 7 H7412 a v c 'f 1 5 l 2 z ,/g f

Rownon Ik, V

m 5A CDE DIN MM5 Charles A. Thomas,

by @Me/mda His Attorney.

Patented Sept. 5, 1950 DYNAMOELECTBIC MACHINE COMMUTATION Charles A. Thomas, Fort Wayne, Ind., assigner to General Electric Com N ew York P lly. a comlation oi' Application March 19, 1948, Serial No.l 15,782

This invention relates to commutating type dynamoelectric machines and lmore particularly to such machines having means arranged to provide a commutating voltage to improve commutation and reduce sparking.

It is well known that the current owing in each armature coil of a commutating type dynamoelectric machine must necessarily reverse itself as to the coil passes from one side of the brush to the other during commutation. In ideal commutation, the current in each coil should decrease at a uniform rate and reach a zero value at a point corresponding to the middle of the brush. The current should then increase at a uniform rate and reach its normal value in the opposite direction by the time the coil passes from under the brush. However, this ideal commutation is ordinarily unobtainable due to the fact that each armature coil, being imbedded in slots in the iron of the armature core, has considerable inductance. Therefore. the coil undergoing commutation has induced in it a voltage of self-induction or a reactance voltage due to the changing current in the coil. This reactance voltage is always in a direction to oppose the change of current and thus proper commutation will not be secured and sparking may result since the current in the coil may not have reached the correct value by the time the coil passes from under the brush. It is, therefore, desirable in the design of commutating type dynamoelectric machines to provide a voltage in the coil undergoing commutation which is opposite to and which will, as nearly as possible, neutralize the reactance voltage during commutation thus insuring that the current in the coil has reached the correct value when the coil leaves the brush. In the past, such a voltage has been produced by shifting the brushes until the coil undergoing commutation comes under a fringe of the main field ux thus providing a generated voltage in the coil of the proper direction and value to neutralize the reactance voltage; or by providing a special commutating field of the right direction and valuel by the means of commutatlng poles or compensating windings.

It is an object of this invention to provide improved means for securing good commutation in commutator type dynamoelectric machines.

Another object of this invention is to provide improved means for reducing brush sparking in commutating type dynamoelectric machines.

A further object of this invention is to provide means for improving commutation and reducing brush sparking incommutating type dynamoelectric machines without the necessity of shifting brushes or providing commutating poles'.

i claim. (ci. 1v1-22s) Further objects and advantages of this invention will become apparent and the invention will be better understood from the following description referring to the accompanying drawing. The features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawing, Fig. 1 illustrates schematically the improved split brush and resistor arrangement of this invention for providing a commutating voltage and Figs. 2 through 6 illustrate schematically the successive stages of commutation of the device of Fig. 1 as the commutator moves past the brush.

In accordance with this invention, there is provided a contact brush having two segements electrically insulated from each other. One segment is connected directly to the circuit of the dynamqelectric machine, while a resistor is arranged in series with the other segment. The voltage drop in this resistor responsive to the ilow of load current in its associated brush segment may be arranged by proper proportioning of the resistor to substantially neutralize the reactive voltage of the coil undergoing commutation. Therefore, the reversal of the current in each coil as it passes from one side of the brush to the other is facilitated and sparking reduced.

Referring now to Fig. 1, there is shown schematically a commutator I of a commutating type dynamoelectric machine Ahaving a. plurality of commutator bars 2. A plurality of armature coils 3 are connected to the commutator bars 2 and arranged in the armature slots in any convenient manner. In the two pole arrangement shown, there are provided two commutator brushes 4 having leading and trailing segments 5 and l respectively abutting the commutator surface. 'I'he two brush segments L5 and 6 are electrically insulated from each other by insulating material 1.

The leading brush segments 5 are directly connected in thel circuit of the dynamoelectric machine by brush leads I. Resistors 9 interposed in series with the leads il of the trailing brush segments l connect these segments to the leading brush leads l. Since both brush segments are arranged to carry load current, it will be readily apparent that a voltage drop will be produced in the resistors 9. This voltage drop, which is responsive to the load current in the trailing brush segment C, may be made by proper proportioning of the resistorsv l to substantially neutralize the reactive voltage'across the armature coil undergoing commutation.

Reference tolFigs. 2 through 6, which show a commutationv cycle and in which like parts are 3 indicated by like numerals, will explain the operation of this invention. Referring now to Fig, 2,

thereisshownaninitialpositionofthebrushl VflowinthecoilAasshownbythearrow." and incoilsC,DandE,asshownbythe arrow I2. It can be readily seen that current II will flow 4 currentwouldnowbeiiowingincoilcatthis pointandthatallofcurrent Il wouldbefiowing through coil connection Il. the voltage drop" acrossthecoilchavingbeendissipatedbythe short circuit current Il. However, as pointed .out above,thechangelnthevalue of the current.

inthiscaeeareductioninthevaluecausedbythe movement of the commutator along the brush, has produced a reactive voltage as indicated by the arrow 28. This reactive voltage tends to maintainafiowofcurrentincoilCin thesame direction as current Il. If a conventional brush through the commutator bar under the brush segment I, through'the brush segment t, the lead Il and the resistor l. The current I2 likewise flows through the commutator bar under the brush segment l. through the brush segment I and the lead l. The currents II and I2 then combine to form the total load current I3.

Referring now to Fig. 3, the commutator is shown as having moved approximately one-half a width of a commutator bar. The current- II is still nowing in the same 4direction in coil A and the current I2 is still flowing in the same direction in coils D and E. Now, however, coils B and C are short circuited by brush segments t and i respectively. Considering now only coil C. there is now provided two parallel paths for the current I2 to reach the brush l, i. e.. through coil connection Il and coil connection Ii. Therefore, only a portion of the current I2 will continue to ilow in the coil C, as indicated by the arrow Ii. the remaining portion of the current.-

as indicated by the arrow I1, flowing through the coil connection I4. The currents It and I1 would be approximately equal in value if it were not for the fact that the coil C is short circuited by the brush 5 and, therefore, a short circuit current I8 will ilow as indicated by the arrow. The current I1 will, therefore, be reduced by the amount of this short circuit currentand the current I6 will be increased by the same amount. The same condition is, of course, obtained in coil B with the current II being divided into components I! and flowing through coil connections I5 and 22 respectively, current 28 being reduced by the amount of short circuit current 2l while current I9 is increased by a corresponding amount. Assuming a position as shown, with the split in the brush 4 in the center of a commutator bar, the current will again divide approximately equally through the brush segments 5 and l.

It would be expected that as the commutator I continues to move in the direction shown, current I1 would increase and current II decrease lmtil a point would be reached, as shown in Fig.

4, where the current I1 would equal current I2 'and current I6 would be reduced to zero due to the short circuiting of the coil C. However, these armature coils being imbedded in the iron of the armature have inductance. The change in the value of the current in the coil as the commutator moves past the brush produces, in accordance with well known principles, a reactive voltage which is in a direction which tends to maintain the flow of current.

Referring now to Fig. 4, the commutator I is shown as having moved another half commutator bar pitch so that the insulation 'I of the brush I is positioned directly over a commutator slot so that no amature coil is short circuited except through resistor 9. It will be noted that current Ii isilowing in coils Aand B and current I2 in coils D and E. It would be expected that no were used, this current might not be completely dissipated by the time coil C has passed out from underthebnxsh.asshowninl"ig.6,inwhich case sparking would result. However. with the split brush construction of this invention with thebrmhsegments l and linsulated by insulation 1, in the position of llig. 4, all of the current II will flow through the trailing segment l, trailing lead Il, and resistor l, while all of the current I2 will now through'the leading segment l and the lead I. The current II ilowing in the resistor l produces a voltage drop indicated by the arrow Il. It will'be readily seen that this voltage dropis in a direction opposite to the reactive voltage Il in coil C. By proper proportioning of the resistor l.' the voltage drop 24 responsive tothe current II can be made to substantialiy neutralize the reactive voltage 2l. Therefore, at this point, there will be no tendency for current to continue to flow in coil C in the direction of current Il.

Referring now to Fil. 5. it will be seen that current II is flowing in coils A and B and current I! is flowing in coil E, the commutator having moved another half bar pitch. Coil C is now again short circuited by brush segment t alone anda portion of current Il flows through coil connection Il, as lindicated by the arrow 2i and another portion through the coil connection Il. as shown by the arrow It. Therefore, current 2l isflowing in coil C, which it will be noted is in the opposite' direction to current I2 which was flowing in coil C in the position of Fig. 2. Since, due to the effect of the split brush and resistor arrangement in the position of Fig. 4, the reactive voltagel was neutralized at that point, there is now no tendency for current to flow in coil C in the direction of current I2. However. due to the increase of the current 2l caused by continual progression of the commutator I in the direction shown, a reactive voltage 21 is developed in the coil C which tends to oppose the increase of the current 2|.

lThis opposition however is overcome by voltage drop of resistor I. Referring now to Fig. 6, the commutator has now moved so that the coil C Is no longer short circuited by the brush segment I. It will' be noted that the commutation cycle of coil C is now completed and the full current II is iiowing therein. the current ilow in coil C having been completely reversed as it traveled across -the brush;

From the foregoing, it will .be readily apparent thatthis invention provides a simple and effective means for neutralizing the reactive f voltage developed in an armature coil while unart. I desire it to be understood, therefore, that this invention is not to be limited to the particular arrangement disclosed and I intend in the appended claims to cover all modifications which do not depart from the spirit and the scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a dynamoelectric machine having a commutator, consisting of a plurality of commutator bars with each of said bars having an armature coil connected thereto, a commutator brush having a plurality of segments of conductive material abutting said commutator, said segments being insulated from each other and having substantially the same resistance, means :for connecting one of said segments directly in the circuit of said dynamoelectric machine, and resistance means having a substantially linear voltage-current characteristic connecting an: other of said segments to said first named connecting means for producing responsive to the current in said other segment a commutating voltage opposed to the reactance voltage across the armature coil short-circuited by said brush whereby said reactance voltage is neutralized and the reversal of current in said coil is facilitated.

2. In a dynamoelectric machine having a commutator consisting of a plurality of commutator bars with each of said bars having an armature coil connected thereto, a commutator brush having two segments of conductive material abutting said commutator, said segments being insulated from each other and having substantially the same resistance, a lead for connecting one of said segments directly in the circuit of said dynamoelectric machine, and a resistor having a substantially linear voltage-current characteristic connecting the other of said segments to said lead for producing responsive to the current in said other segment a commutating voltage drop opposed to the reactance a substantially linear voltage-current characteristic connecting the other of said segments to said lead for producing responsive to the current in said other segment a commutating voltage drop opposed to the reactance voltage across the armature coil short-circuited by said brush whereby said reactance voltage is neutralized and the reversal of current in said coil is facilitated.

5. In a dynamoelectric machine having a commutator consisting of a plurality of commutator bars With each of said bars having an armature coil connected thereto, a commutator brush having two segments of conductive material abutting said commutator and having substantially the same resistance, insulation means for separating said segments, a lead for connecting the leading brush segment directly in the circuit of said dynamoelectric machine, and a resistor having a substantially linear voltage-current characteristic connecting the trailing brush segment to said lead for producing responsive to the current in said trailing segment a commutating voltage drop opposed to the reactance voltage across the armature coil short-circuited by said brush wherebyv said reactance voltage is neutralized and the reversal of current in said coil is facilitated.

6. In a dynamoelectric machine having a commutator consisting of a plurality of commutator bars with each of said bars having an armature coil connected thereto, a commutator brush hav- Y ing two segments of conductive material abutting voltage across the armature coil short-circuited by said brush whereby said reactance voltage is neutralized and the reversal of current in said coil is facilitated.

3. In a dynamoelectric machine having a commutator consisting of a plurality of commutator bars with each of said bars having an armature coil connected thereto, a commutator brush having two segments of conductive material abutting said commutator and having substantially the saine resistance, said segments being insulated from each other, a lead for connecting the leading brush segment directly in the circuit of said dynamoelectric machine, and a resistor having a substantially linear voltage-current characteristic connecting the trailing brush segment to said lead for producing responsive to the current in said trailing segment a commutating voltage drop opposed to the reactance voltage across the amature coil short-circuited by said brush whereby said reactance voltage is neutralized and the reversal of current in said coil is facilitated.

4. In a dynamoelectric machine having a commutator consisting of a plurality of commutator bars with each of said bars having an armature coil connected thereto, a commutator brush having two segments of conductive material abutting said commutator and having substantially the same resistance, insulation means for separating said segments, a lead for connecting one of said segments directly in the circuit oi' said dynamoelectrical machine, and a resistor having 76 2,152,327

said commutator and having substantially the same resistance, insulation means for separating said segments, leads for connecting said segments in the circuit of said dynamoelectric machine, and a resistor having a substantially linear voltage-current characteristic interposed in series relationship with one of said leads and its associated brush segment for producing responsive to the current in said one lead a commutating voltage drop opposed to the reactance voltage across the armature coil short-circuited by said brush whereby said reactance voltage is neutralized and the reversal of current in said coil is facilitated.

7. In a dynamoelectric machine having a commutator consisting of a plurality of commutator bars with each of said bars having an armature coil connected thereto, a commutator brush having two segments of conductive material abutting said commutator and having substantially the same resistance, insulation means for separating said segments, leads connecting the leading and trailing brush segments in the circuit of said dynamoelectric machine, and a resistor having a substantially linear voltage-current chai'- acteristic interposed in series with the trailing brush lead and trailing brush segment for producing responsive to the current in said trailing brush segment lead a commutating voltage drop opposed to the reactance voltage across the aimature coil short-circuited by said brush whereby said reactance voltage is neutralized and the reversal of eurent in said coil is facilitated.

CHARLES A. THOMAS.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,059,134v Fornander Apr. 15, 1913 1,884,021 Ludwig et al Oct. 25, 1932 Rauhut Mar. 28, 1939 

